1. Technical Field
The present invention generally relates to a circuit for generating a proportional to absolute temperature (PTAT) current and, more particularly, to a circuit for generating a dual-mode PTAT current based on a voltage reference.
2. Background
Bandgap voltage references are used in a variety of integrated circuits, electronic devices and electronic systems that require a stable voltage reference over a range of temperatures and process variations. For example, many data acquisition systems, voltage regulators and measurement devices utilize bandgap voltage reference circuits to provide a stable voltage reference to serve as a comparison basis for other supply and/or input voltages. Although traditional bandgap voltage reference circuits may generate bandgap voltages exhibiting little variation over a nominal range of operating temperatures, higher-order device characteristics, such as device voltages and currents that vary nonlinearly with temperature, can cause the generated bandgap voltage to vary substantially at temperatures outside the nominal temperature range.
In the traditional design, an oscillator generates a frequency independent of temperature, which means that even the temperature changes, the oscillator generates a constant frequency. If it is required to generate two frequencies at different temperatures, it may be needed to generate two control currents dependent of temperature in order to control an oscillator to generate the frequencies.
Some bandgap voltage reference circuits, in an attempt to address the above-mentioned issue, have been developed. For example, U.S. Pat. No. 7,728,575 disclosed an apparatus including a low temperature correction circuit and a high current correction circuit for higher-order correction of bandgap voltage references. However, the apparatus may be complex and not cost efficient. Moreover, U.S. Pat. No. 6,922,045 disclosed a current driver circuit to generate temperature compensated currents. However, the architecture may still be complex and not flexible.